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Abstract

A technique is described whereby an advanced self-aligned bipolar transistor process (Atx/Ntx compatible) process depends on the structures provided by molecular beam epitaxy (MBE) to grown an NPN profile. By optimizing the upward mode operation of the intrinsic profile, high performance bipolar transistors are produced.

Country

United States

Language

English (United States)

This text was extracted from an ASCII text file.

This is the abbreviated version, containing approximately
52% of the total text.

Upward Operating Molecular Beam Epitaxy Bipolar
Transistors

A technique
is described whereby an advanced self-aligned
bipolar transistor process (Atx/Ntx compatible) process depends on
the structures provided by molecular beam epitaxy (MBE) to grown an
NPN profile. By optimizing the upward
mode operation of the
intrinsic profile, high performance bipolar transistors are produced.

Si-based MBE
applications have often been hindered by the
concern for defect creation and propagation of grown-on-patterned
wafers, which is the typical result created by selective oxidation,
implantation and diffusion processes.
Conversely, if the MBE takes
place at the beginning of the device fabrication process on a
non-patterned surface, considerations and problems faced can be
summarized as follows:

Full low temperature isolation must be available.

Contacting the
different layers (base, collector) must be
achieved through etching. The lack of selectivity of Reactive Ion
Etching (RIE) makes it extremely difficult
to stop on a very thin, <
100 nm, base. This is one of the major reasons for going to
an MBE
process.
Homojunction, heterojunctions are considered separate
issues.
Using chemical etchants may provide the needed vertical
selectivity, but will cause undercuts
and thus linewidth control
and edge coverage problems.

MESA
structures have severe topography and are therefore
difficult to interconnect over large areas.

The concept
described herein provides a method of optimizing
the intrinsic profile for upward operation and thereby relieves the
aforementioned etching and topography problems.
A low temperature
deep trench process is still required if MBE growth is preferred on a
blanket substrate. The conventional Atx
or Ntx process can be used
to contact the base from the top, such as the base-collector
junction. The concept allows for very
thin base-widths, avoids
poly-emitter contact resistance problems and can result in improved
density of an Emitter Coupled Logic (ECL) gate layout.

The process involves seven fabrication steps:

1. Grow the
vertical profile on a blanket substrate, with thick
emitter on the bottom, thin graded
base and approximately 100 to
200 nm of lightly doped collector, as
shown in Fig. 1a. Fig. 1b
illustrates the vertical profile growth on
the blanket substrate.

2. Next, it is
assumed that both a deep and shallow trench can be
formed in a low temperature
process. ...